Which of the following cardiac defects is the MOST common congenital heart lesion associated with Down syndrome?

Explanation

## Cardiac Manifestations of Down Syndrome **Key Point:** Atrioventricular septal defect (AVSD) is the most characteristic and frequent congenital heart defect in Down syndrome, occurring in 40–50% of children with cardiac involvement. ### Cardiac Defects in Down Syndrome — Frequency and Features | Cardiac Lesion | Frequency in DS | Notes | Pathophysiology | | --- | --- | --- | --- | | **AVSD (Endocardial cushion defect)** | 40–50% of cardiac DS | Pathognomonic for DS; involves AV valves and septa | Failure of endocardial cushion fusion; results in AV valve regurgitation and shunting | | **VSD** | 30–35% of cardiac DS | Common but not specific to DS | Defect in ventricular septum; left-to-right shunt | | **Tetralogy of Fallot** | 10–15% of cardiac DS | Right-sided lesion; cyanotic | Conotruncal abnormality | | **PDA** | 5–10% of cardiac DS | More common in premature infants | Failure of ductus arteriosus closure | | **Atrial septal defect (ASD)** | 5–10% of cardiac DS | Ostium secundum type most common | Defect in atrial septum | **High-Yield:** AVSD is so strongly associated with Down syndrome that its presence in a neonate should prompt immediate karyotyping or chromosomal microarray analysis. ### Clinical Features of AVSD in Down Syndrome 1. **Anatomy:** Deficiency of endocardial cushion tissue → primum ASD + inlet VSD + cleft mitral and/or tricuspid valve 2. **Hemodynamics:** Left-to-right shunt → pulmonary overcirculation → heart failure 3. **Presentation:** Failure to thrive, recurrent respiratory infections, poor feeding, hepatomegaly 4. **Auscultation:** Holosystolic murmur (mitral regurgitation), diastolic murmur (tricuspid regurgitation), fixed split S₂ 5. **Management:** Surgical repair typically performed by 6–12 months of age to prevent pulmonary hypertension **Clinical Pearl:** All infants with Down syndrome require echocardiography within the first weeks of life, as ~50% have cardiac involvement and early detection allows timely surgical intervention. **Mnemonic:** **AVSD in DS** — Remember that AVSD (atrioventricular septal defect) is the signature cardiac lesion of Down syndrome; it is much rarer in the general population but highly prevalent in trisomy 21.